We have found that the dimorphic fungus Candida albicans produces a soluble substance that controls dimorphism. This morphogenic auto-regulatory substance (MARS) keeps the organism in the yeast phase. Because yeast (Y) to mycelial (M) phase conversion may be important in the pathogenesis of disease (candidiasis) due to C. albicans we hope to gain an understanding of phase or form regulation through studies on MARS. Purification and chemical-physical characterization of MARS will be done using various forms of chromatography, electrophoresis, and NMR and mass spectroscopy. To study the interaction of the regulatory substance with C. albicans, radiolabeled MARS will be prepared, allowed to interact with C albicans and analyses will be done to determine if the interaction takes place primarily at the level of the cell wall, cell membrane or protoplasm. Specificity of interaction will be defined by similar studies on isolated mutants of C. albicans that are unaffected by MARS. To determine if MARS is produced in vivo, mice will be injected with C. albicans in a localized site, fluids will be recovered, and the presence of MARS will be detected by biologic testing and by a competitive binding radioimmunoassay (RIA) technique. The effect of rabbit antibodies specific for MARS on in vitro Y yields M form conversion will be examined as well as the in vivo effect of anti-MARS on candidal lesion development.